1. Field of the Invention
The present invention relates to a non-contact charger which uses electromagnetic induction to transmit electrical power between a primary coil and a secondary coil which are independent of each other.
2. Description of the Related Art
A non-contact charger comprises a primary side circuit and a secondary side circuit, which are independently mounted inside a case, and must efficiently transmit a large amount of electrical power from the primary side circuit to the secondary side circuit. An important factor in accomplishing this is to increase the magnetic transmission efficiency.
One conventional method of increasing the magnetic transmission efficiency is to use U-shaped magnetic cores as the primary side and secondary side coils. The coils are divided and wound around magnetic legs at each end, thereby increasing the size of the magnetic leg faces of the opposing magnetic cores and the opposing faces of the coils.
With regard to magnetic transmission efficiency, it is effective to increase the cross-sectional area of the magnetic core and the coil in the secondary side circuit. However, due to the demand for small-scale and portable devices, there are limits on the size of this area, and also on the sizes of the magnetic core and coil which can be mounted in the secondary side case, consequently limiting the power which can be transmitted. FIG. 4 shows a conventional small-scale portable non-contact charger.
In FIG. 4, reference code A represents a primary side coil, and reference code B represents a secondary side coil. Reference code 11 represents one section of the case of the primary side coil A, reference code 12 represents a U-shaped magnetic core used in the primary side coil A, reference code 13 represents a winding which is wound around the magnetic leg of the U-shaped magnetic core 12 of the primary side coil A, reference code 14 represents one section of the case of the secondary side coil B, reference code 15 represents a U-shaped magnetic core used in the secondary side coil B, and reference code 16 represents a winding which is wound around the magnetic leg of the U-shaped magnetic core 15 of the secondary side coil B. The primary side coil A and the secondary side coil B are formed by winding the windings 13 and 16 around the magnetic legs at each end of the magnetic cores 12 and 15, and arranging the magnetic legs so as to face each other with the cases 11 and 14 therebetween.
FIG. 5 shows the distribution of magnetic flux in this constitution, and uses the same reference codes as those in FIG. 4.
In FIG. 5, magnetic flux is generated in the primary side coil A, and follows a path around the magnetic legs 12a and 12b on each side of the U-shaped magnetic core 12, around the magnetic legs 15a and 15b at each end of the U-shaped magnetic core 15 of the secondary side coil B, thereby forming a closed magnetic path for transmitting power to the secondary side coil B.
One conceivable method for improving the magnetic coupling between the primary side coil A and the secondary side coil B is to increase the cross-sectional areas of the magnetic legs 12a, 12b, 15a, and 15b of the magnetic cores 12 and 15 of the secondary side coil B and the primary side coil A in order to transmit as much of the magnetic flux as possible from the primary side coil A to the secondary side coil B. The distance between the magnetic legs 12a and 12b (open end sides) at each end of the primary side coil A could also be increased to prevent the magnetic flux from passing through the secondary side coil B, thereby reducing the magnetic flux (leaked flux) x which returns directly to the primary side coil A.
However, since the winding 16 is wound around the magnetic legs 15a and 15b at each end of the U-shaped magnetic core 15 of the secondary side coil B, consideration must be given to providing a space for the winding 16. For this reason, it is extremely difficult to increase the cross-sectional areas of the magnetic legs 15a and 15b, and to increase the distance between the magnetic legs 15a and 15b at each end of the U-shaped magnetic core 15, in portable electronic devices which must be made thin and small.
It is an object of the present invention to provide a non-contact charger wherein the secondary side coil can be made small and thin, and having increased magnetic transmission efficiency.
In order to achieve the above objects, the present invention provides a non-contact charger wherein a battery-driven electronic device containing a secondary battery is provided in a power supply section and electrical power is supplied thereto by non-contact, the non-contact charger comprising a primary side coil, which supplies power by electromagnetic induction, and a secondary side coil, which receives power, the primary side and secondary side coils provided facing each other with cases therebetween; the primary side coil comprising a U-shaped magnetic core having a leg at each end thereof, and windings which are wound around the magnetic legs; and the secondary side coil comprising a U-shaped magnetic core having a leg at each end thereof, and a winding which is wound around a common magnetic core of the U-shaped magnetic core; the cross-sectional area of the magnetic legs of the primary side coil being greater than the cross-sectional area of the magnetic legs of the secondary side coil.
In the secondary side coil, the distance between the open ends of the magnetic legs of the magnetic core is greater than the common magnetic core, and, in the primary side coil, the base section of the cross-sectional area of the magnetic legs of the magnetic core is wider than the tip section thereof Therefore, magnetic flux, generated in the primary side coil, is efficiently supplied to the secondary side coil.
Further, a braided wire is used as the material for the winding of at least one of the primary side coil and the secondary side coil.
According to the non-contact charger of the present invention, a battery-driven electronic device containing a secondary battery is provided in a power supply section and electrical power is supplied thereto by non-contact. The non-contact charger comprises a primary side coil and a secondary side coil, the primary side coil supplies power to the secondary side coil by electromagnetic induction. The primary side and secondary side coils face each other with a case therebetween. The primary side coil comprises a U-shaped magnetic core having a leg at each end thereof, and windings which are wound around the magnetic legs. The secondary side coil comprises a U-shaped magnetic core having a leg at each end thereof, and a winding which is wound around a common magnetic core of the U-shaped magnetic core. The cross-sectional area of the magnetic legs of the primary side coil is greater than the cross-sectional area of the magnetic legs of the secondary side coil.
In the secondary side coil, the distance between the open ends of the magnetic legs of the magnetic core is greater than the common magnetic core, and, in the primary side coil, the base section of the cross-sectional area of the magnetic legs of the magnetic core is wider than the tip section thereof. Therefore, the secondary side coil can be made small, light, and thin, and can obtain the required power.
Furthermore, a braided wire, which is made by braiding cluster wires, each comprising multiple insulated single-wires, so that the positions of the cluster wires change alternately inside and outside, is used as the material for the winding of at least one of the primary side coil and the secondary side coil. Therefore, when the magnetic flux generated by one of the coils has intersected with the winding of the other coil without passing the magnetic core of the other coil, loss resulting from the eddy current of the other coil can be reduced, helping to reduce loss in the secondary side coil and supply the required power.